1. Field of the Invention
The present invention relates to an electrophotographic copying apparatus of an arrangement in which a copy board carrying an original to be copied is reciprocatably moved relative to a main body of the copying apparatus and adapted to cooperate with an optical system provided at a fixed position in the apparatus thereby to produce a latent image of the original to be copied on a photosensitive medium. More particularly, the present invention concerns a mechanism for releasably coupling the copy board to a driving mechanism or system therefor.
Although the mechanism or apparatus according to the invention can be effectively applied to copying apparatus either of the image transfer or electrofax type, it is assumed in the following description for convenience of illustration that the invention is applied to copying apparatus in which the image transfer process is carried out.
2. Description of the Prior Art
As is well known, a drum-like light sensitive medium is increasingly employed as the latent image forming medium in commercially available copying apparatus in an attempt to reduce the size of the copying apparatus and/or enhance the operating performance thereof. The drum-like light sensitive medium is usually implemented in one of at least three configurations described below:
In the first configuration, an electrically conductive drum surface formed of aluminum or the like is wholly coated with a photo-electric semiconductor layer such as selenium, cadmium sulfide or the like. The drum of this type is referred to as the demand type light sensitive drum.
In the case of the second configuration, a predetermined zone of the drum surface is covered with a web-like light sensitive sheet formed of zinc oxide. The web-like light sensitive sheet is wound on a supply spool and dispensed progressively for use, to be finally wound up by a take up spool.
According to the third configuration, a sheet-like sensitive paper is detachably applied onto the drum surface at a predetermined region and replaced by a fresh sheet after a predetermined number of repeated uses.
However, in hitherto known copying apparatus in which the drum of the third configuration described above is employed, the replacement of the light sensitive sheet requires extraction of the drum outwardly from the copying apparatus, involving time-consuming and troublesome procedures, because the drum is positioned within the main body of the copying apparatus with a high accuracy and is surrounded by a number of various processing or treating means.
As an attempt to solve the above problem, it is conceivable that a machine frame (a top plate positioned below the copy board) be releasably mounted to the main body of the apparatus. For replacement of the light sensitive sheet, a printing button switch is actuated to move the copy board for a predetermined distance. Thereafter, the top plate is removed to allow the replacement of the light sensitive sheet through the now available opening. However, because a main switch must be turned off in the course of actuation of the printing button in order to stop the copy board, a troublesome procedure is involved. Furthermore, the charging electrode and the irradiating lamp are energized during the movement of the copy board. Accordingly, when the main switch is turned on again after the replacement of the light sensitive sheets, the charging electrode and the irradiating lamp are again energized, as a result of which electric energy is consumed wastefully during each replacement of the light sensitive sheet. Where the copied paper (sometimes referred to as the transfer sheet or copy sheet) is discharged from a top portion of the copying apparatus (irrespective of the configuration of the light sensitive drum) as is shown in FIG. 1, the copy sheet is difficult to remove forwardly of the apparatus when jamming occurs in the region between an image transferring station and a sheet discharging station. It is a fact that the more compact the machine is, the more difficult is sheet removal. Of course, the jammed copy sheet may be taken out after removal of the top plate. However, in this case, a similarly troublesome procedure as those required for the replacement of the light sensitive sheets is disadvantageously involved. The above also applies to replacement of the exposure lamp L.
The disadvantages of the hitherto known apparatus are obviously ascribable to the configuration of the light sensitive drum as well as the location of the sheet discharging portion. And it is also true that the coupling mechanism between the copy board and the driving system provides a cause for such disadvantage. In this connection, it is noted that in the case of prior art copying apparatus, a pulley having a diameter substantially equal to that of the drum is mounted on the supporting shaft for the drum. A steel cord having an end secured to a front portion of the copy board is reeled around the pulley for a predetermined length with the other end of the cord being secured to a rear end portion of the copy board. An electromagnetic clutch is interposed in the driving system including the pulley and the steel cord, whereby the reciprocation of the copy board is controlled by means of the magnetic clutch. With such arrangement, the free movement of the copy board is considerably restricted. In addition, even if an optimum tension is applied to the cord at the time of assemblying the copying apparatus, the copy board may possibly exhibit unstable movement at a variable speed at a starting point of the copying operation, making highly accurate control difficult.